1. Field of the Invention
The present invention relates generally to a recording method and a recording apparatus for recording information including characters, images, pictures, and the like on a recording medium. Also the present invention relates to an information-processing system such as a copying machine, a facsimile machine, a printer, a word processor, and a personal computer, using such an apparatus as its output device.
2. Description of the Related Art
Heretofore, various kinds of serial-type recording apparatuses have been proposed as in the form of mounting the recording head of a wire dot matrix recording system, thermal recording system, thermal transfer recording system, ink jet recording system, or the like. The recording apparatus comprises a mobile device (hereinafter referred to as a carriage) on which the recording head is mounted for performing an image formation on a recording medium such as a sheet of paper, a piece of fabric and a sheet of plastic material for overhead projector (generally called an OHP sheet in Japan). For driving the carriage, in general, the serial-type recording apparatus further comprises a motor (mostly, a stepping motor) as a driving means.
In the following description, we will explain an ink jet recording apparatus to serve as an example for explaining a configuration of the conventional recording apparatus and its driving means and control system.
Among the conventional recording methods, the ink jet recording methods have been known as one of the non-impact methods and they are mainly grouped into two different types in that they prepare ink droplets and generate energies for ejecting the ink droplets in different manners. That is, one is of a continuous type and the other is of an on-demand type. The continuous type methods are further grouped into a charge particle control type and a spray type, while the on-demand methods are further grouped into a piezo type, a spark type, and a bubble jet type.
In the case of the method of a continuous type, a plurality of ink droplets is ejected continuously but only a required part of them is charged so as to be adhered on the recording medium but the others are of no use. In the case of the method of on-demand type, on the other hand, ink droplets are ejected when they are required for the recording process. By this method, therefore, the ink can be used without causing any useless droplets and without staining an interior of the apparatus. According to the method of on-demand type, furthermore, a response frequency of the recording means is lower than that of the continuous one because the on-demand type recording head starts and stops its ink ejection during the period of image formation. It follows from this that the high speed recording can be attained by increasing the number of nozzles of the recording head in the type of on-demand, so that a lot of recording apparatuses being commercially available are of the on-demand type.
Therefore the ink jet recording apparatus comprising the recording head of such ink jet type has been commercially manufactured and used to meet the needs for high speed recording, high resolution, high image quality, low noise, and so forth. That is, the ink jet type recording apparatus has thus been employed as printers for copy machines, facsimiles, printers, word processors, output terminals of work stations and so forth, handy or portable printers to be employed in personal computers, host computers, optical disk systems, video systems, and so forth. In these cases, the ink jet recording apparatus can be constructed and designed so as to match their individual mechanisms, operation or service conditions, and the like.
The ink jet recording apparatus generally comprises: a carriage for carrying a recording means (i.e., a recording head) and an ink tank; a transfer means for transferring a recording medium (e.g., a sheet of recording paper); and a control means for controlling the drive of these means. In the ink jet recording apparatus, the ink jet recording head performs its serial scanning movement (i.e., the head scans over a surface of the recording head sequentially) along the direction (main-scanning direction) perpendicular to the direction (sub-scanning direction) of transmitting the recording medium for ejecting ink droplets from a plurality of ejection orifices, while the recording medium is intermittently shifted at a distance corresponding to a recording width of the recording medium.
The process of ink jet recording is characterized by ejecting ink droplets on the recording medium in accordance with the recording signals, so that it has been widely applied in various systems as a noiseless recording process with an inexpensive running cost. By using the recording head comprising a plurality of ink-ejecting nozzles linearly arranged in the sub-scanning direction, an image having a width thereof corresponding to the number of the nozzles can be recorded by a single scanning movement of the recording head. Consequently, high-speed recording movement can be attained.
As described above, however, the aforementioned conventional recording apparatus uses in general the motor (mainly the step motor, i.e., pulse motor, to be revolved in accordance with input pulse) as a driving means for driving the carriage. The motor is responsible for shifting a position of the carriage in the main-scanning direction with respect to the recording medium. On this occasion, in general, the motor is set into rotation at a constant rate by producing an acceleration, i.e., by gradually increasing the speed of rotation. In the conventional recording apparatus, furthermore, a failure of driving the carriage ordinarily at a constant rate (i.e., situations in which acceleration varies) would create instability in image qualities, especially just after the carriage reaches at the predetermined recording rate from a rest state of the motor. For decreasing the instability in image qualities in most of the conventional recording apparatuses, therefore, prior to the recording of image, a recording speed of the carriage is kept at a constant by accelerating from the rest state to the predetermined level to attain the recording speed. By the way, a time interval from rest is required to attain a constant recording speed after accelerating the carriage. The time interval becomes longer when the recording speed is higher than that of the usual, with the result that an approach run of the carriage for the recording movement requires a longer area. It means that a recording area of the recording medium decreases with increase in the recording speed. Thus a problem to be solved is to increase the recording speed without decreasing a recording area of the recording apparatus.
FIGS. 1 and 2 show the time variation of the carriage's velocity for explaining a typical acceleration of a carriage-driving motor (e.g., a magnetic stepping motor) at the period of driving the carriage to be installed in the conventional ink jet recording apparatus. In these figures, the vertical axis is for a transport velocity of the carriage and the horizontal axis is for a lapse of time.
For transporting the carriage by driving the magnetic stepping motor, the so-called open loop control is generally used in such driving. In this case, a detection of the carriage's position is not performed after sending a control signal to the motor. Therefore we cannot detect whether the motor or the carriage is being driven in accordance with the control signal.
In FIGS. 1 and 2, control values of the carriage's velocity at successive times, which are experimentally obtained, are plotted as a thick line D, while each control value practically obtained is plotted as a narrow line (E). In the case of an example as shown in FIG. 1, the carriage's motion is controlled as a uniformly accelerated linear motion. Therefore the carriage's velocity is constantly increased to a predetermined velocity (i.e., a control value) Vk and then the carriage's velocity is kept at a constant without deviating from that value Vk by means of controlling a drive of the carriage motor. In spite of such control, however, an actual position of the carriage is deviated from the expected position with respect to the control value Vk because of variations occurring in the carriage's velocity at successive times. That is, just after the acceleration the carriage once travels at a velocity of over Vk. Then the carriage's displacement can be successively performed at higher and lower velocities in a repetitive manner, with respect to the control value Vk. This kind of variation in the carriage's velocity can be observed in spite of passing the carriage over the point of starting the recording movement.
FIG. 2 shows an example of controlling the carriage's motion by means of a combination of exponential components instead of using the uniformly accelerated linear motion. In this case, however, variations in the carriage's velocity can be also observed after the carriage's acceleration, in spite of passing over the recording start position.
If the variation in the carriage's velocity is continued after starting the recording of an image on a recording medium, the resulting image can be disrupted. To solve this problem, it has been required to converge the above variations during the period between the end of acceleration and the start of recording.
During the period between the time of starting the recording movement and the time of ending the acceleration, the carriage tends to locate on the far side of each expected position at the successive times. In this case, it is noted that the extent to which the carriage's location is deviated from the expected position with respect to the velocity is gradually enlarged with the time, involving that the extent of variations in the carriage's velocity is also enlarged.
At the time of starting the acceleration, the carriage receives a force of the following equation: EQU F=Ma
(where "F" denotes a force, "M" denotes a weight of the carriage, "a" denotes an acceleration).
When the force F is applied on the carriage at a moment of starting the acceleration, the carriage starts to move at a velocity slower than the above control level Vk for a very short period because of stretching a belt member or of hardness of other members for transporting the carriage. After that short period, the carriage moves at a velocity higher than the above control level because of a repulsion force to bring back the shape of the belt member or the like. When the repulsion force is not enough, the acceleration can be finished with a delayed movement of the carriage, depending on the configuration of the transport device. A degree of the force F to be applied on the carriage at the time of accelerating the carriage's motion is directly proportionate to the degree of acceleration, so that the above variations in the carriage's velocity can be converged by decreasing the acceleration. However, it requires a comparatively larger device for providing a longer distance to accelerate the carriage's motion.
Accordingly, it has been required to finish the acceleration of the carriage's motion within a short period by rapidly accelerating the carriage.